There is a case, I submit, for urging all politicians to steer clear of metaphors: success in politics relies largely upon obscurity, obfuscation and no one actually understanding what the hell you're going on about, whereas the whole point of a metaphor is that it paints a vivid image that speaks powerfully, memorably and unambiguously to everyone. Even the greatest political writers and orators tend to use metaphor sparingly, for fear of getting it wrong. And as upstanding a man as John Prescott certainly is, few would describe him as a great political writer and orator.

No doubt the former ship's steward meant well when he sprang to the PM's defence on a Labour blog, declaring that calls for a "new captain" were unnecessary because "it wasn't the captain that sank the Titanic - a ship they claimed was unsinkable - it was the iceberg. The best way to avoid disaster is to manage your way around the problem."

What he intended to say, presumably, was that the party should stop squabbling, unite behind its beleaguered skipper, and trust him to pilot HMS Great Britain through the storm to calmer waters beyond. What he actually did was liken Labour to a supposedly invincible luxury cruise liner that soon after its much-feted launch found itself transformed into world's best-known maritime disaster.

There's worse, though. Some argue that the real captain of the Titanic, Edward J Smith, who went down with his ship, might have done more to avoid the fatal collision (which can only be interpreted, obviously, as a crushing electoral defeat) by slowing down and steering an even more southerly course (or adopting, perhaps, a few decent new policies). And what is certain is that several clear warnings from other ships of lethal icebergs ahead failed, for various reasons, to reach the officers on the Titanic's bridge (or national executive committee).

Thus, through the use of a single unfortunate metaphor, has one of Labour's most loyal supporters suggested to everyone who didn't already know it that the good ship Labour is, well, doomed. Rather like when Hillary Clinton, during her recent campaign for the Democratic presidential nomination, said that for her to heed calls to abandon her bid prematurely would be like Rocky getting "halfway up those art-museum steps and saying, 'Well, I guess that's about far enough.'"

Rocky, you may recall, lost his final fight on a split decision. Politicians: steer clear of metaphor.